He was not out of mind, however, and Djokovic was quick to pay tribute to his father after his gritty victory over world number two Federer, winner of the title for the past two years.

"It's been a very long year, a very long two years, but very successful two years," five-times Grand Slam champion Djokovic, who ended a second consecutive season as world number one having won a career best 75 matches, said.

"I didn't really know how I would follow up after my incredible 2011, but I believed that I have to use the time where I'm playing the best tennis of my life.

"It was a fantastic year, where I've had to face a lot of difficulties off the court as well. Especially coming into this tournament, having my father fighting his own fight for health gave me extra strength that I wanted to play for him in a way.

"That's one of the reasons I really gave it all every match, especially tonight. This was a title for him."

'I believe that this year has been even more successful for me'

Djokovic's father has been seriously ill with a respiratory problem and Djokovic has spent hours on the phone over the past eight days monitoring his progress.

It makes his achievement of marching to the title undefeated, having won all his round-robin matches, including one against US Open champion Andy Murray, even more impressive.

"I actually feel even more satisfied right now than last year, even though I had an incredible 2011," the 25-year-old, who won three of the four majors last year after starting the season with a 43-match winning streak, said.

"I feel this year, considering the circumstances that I had to face on and off the court, expectations, all these things, I believe that this year has been even more successful for me."

Image: Novak Djokovic of Serbia lifts the trophy after the men's singles final against Roger Federer of Switzerland at the ATP World Tour FinalsPhotographs: Michael Regan/Getty Images